Darkbird to answer your question for the three weeks ive had them, looks like they haven't even touched the washers maybe they dont notice the oppertunity yet but mine are hot glued on and i check them for any type of play when i refill the bottle and as of yet still really secure and tight to tub wall. the washers i use for large 16 oz bottles have a 1/2 inside diameter. as far as part number i dont think the ones i have will help you but you can measure the the inside diameter and if your using the 16 oz use the 1/2 in diameter, for the smaller bottles 3/8 in inside diameter will all give you snug fit with no gaps. anyways hope that helps i didnt know sizes i needed so i grab a big range from work and found these two what you would need.